Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$20.42	3.635%	$21.1623	$21.16	$21.15	$21.20
Purchase #2	$25.50	6.423%	$27.1379	$27.14	$27.15	$27.10
Purchase #3	$144.31	4.532%	$150.8501	$150.85	$150.85	$150.90
Purchase #4	$112.62	13.262%	$127.5557	$127.56	$127.55	$127.60
Purchase #5	$81.98	13.524%	$93.067	$93.07	$93.05	$93.10
Purchase #6	$238.79	3.246%	$246.5411	$246.54	$246.55	$246.50
Purchase #7	$131.33	3.154%	$135.4721	$135.47	$135.45	$135.50
7 purchase totals =	$754.95		$801.7862	$801.79	$801.75	$801.90